Integrated resistances in semiconductor circuitry normally have a relatively high level of temperature dependency. However, it may be desirable to provide an integrated resistance in temperature-independent or temperature-compensated fashion. Such resistances which are insensitive to temperature are used, inter alia, in high-accuracy transconductance amplifiers, high-accuracy transimpedance amplifiers and in applications in medical engineering, for example in measuring equipment for blood sugar content.
Pages 248 to 250 in chapter 5.2 of the document by D. A. Johns, K. Martin: “Analog Integrated Circuit Design”, Toronto, Ontario, Canada, Wiley 1997 indicate how to provide on-chip resistances in thermally stable fashion. In this document, the transconductance of an operational amplifier is stabilized by virtue of there being a high-accuracy, thermally stable external resistance in the form of a non-integrated, discrete component.
The document by A. McLaren and K. Martin: “Generation of Accurate On-Chip Time Constants And Stable Transconductances”, IEEE Journal of Solid-State Circuits, Vol. 36, No. 4, April 2001 proposes a development of this principle such that an on-chip resistance is used instead of the external reference resistance. For the purpose of calibrating this resistance, complex analog circuitry is provided and also there is a need for a variable bias resistance split into numerous, parallel-connected elemental resistances, graduated in binary and thermometer code, see FIG. 5 therein.
With a temperature variation of around 60° Celsius, the transconductance scatter for this principle is nevertheless around 2.2%. Added to this is the fact that the convergence for such a circuit is relatively slow.